Pressure-medium actuated friction disk clutch or brake

ABSTRACT

A pressure-medium actuated friction disk clutch or -brake is provided having a piston/cylinder actuation unit (1,2) and a disk spring (3) arranged between the piston (1) and a pressure plate (4) of the friction disk clutch, whereby the binding surfaces (11, 41) for the disk spring (3) are generally perpendicular to the axis (A) of the friction disk clutch. In order to influence a characteristic force curve (K1, K2) at the closing of the friction disk clutch (4, 5, 6, 7), at least one of the binding surfaces (11, 41), has a definitely shaped, radially extending contour (R1, R2, R4, 13) deviating from the right angle. Due to the modified angle of attack and the rolling off of the contact point of the disk spring on the binding surface and the therewith connected shortening of the lever arm (H), any desired pressure characteristic can be achieved with a normally built disk spring. Placing a contour at the binding surface of the piston (1) and/or the pressure plate (4) is simple and cost-effective.

FIELD OF THE INVENTION

The invention relates to a pressure-medium actuated friction disk clutchor brake.

THE RELATED ART

German Patent 25 40 191 discloses a pressure-medium actuated frictionclutch wherein a disk spring is arranged between a clutch and anactuation device. This spring is prestressed between a pressure plate ofthe friction disk clutch and a slide disk, by means of a limit screw. Ina rest closed position of the friction disk clutch, when it is not underthe action of a pressure medium, the frictional coupling of the frictiondisk takes place depending on the layout of the disk spring.

German Patent 34 41 815 discloses a pressure-medium actuated frictiondisk clutch, wherein-between the pressure plate of the friction diskclutch, an axially fixed shaft and a piston of the actuation device -adisk spring is arranged which is conically shaped in cross section andhas three radially staggered contact surface. The effectivecharacteristic curve of the spring at the closing of the friction diskclutch is achieved due to the particular shape of the disk spring incross section, to the arrangement of several disk springs with equaldiameter, or only with an outer- or inner equal diameter, or due to disksprings having a plurality of square or slot-like cutouts, which can belocated on the inner- as well as the outer diameter of the disk spring.The disk spring might help reduce the impact effect at the engagement ofthe friction disk clutch and also make possible an adjustment in thedesired sense during the closing process, as well as accelerating thelatter in comparison with the solution offered by German Patent 25 40191. However, such spring or springs with a particular shape andconfiguration are expensive in comparison to standard spring and oftenalso have a considerably shorter life. Besides, possible necessary highforces can not be transmitted.

From U.S. Pat. No. 3,266,608, a friction disk clutch is known, whereinthe binding surface at the pressure plate has a special configuration.

The configuration of this binding surface, however, serves exclusivelythe purpose of insuring the adherence of the disk spring to the ring 92in the open position of the clutch and to make possible a reversal ofthe travel direction of the disk spring during the closing process.Thereby, the partial flow of the pressure medium provided for a gentleengagement of the clutch is closed off via the disk spring and the plate116. The gentle engagement of the clutch and the modification of thecharacteristic force curve by the disk spring is not achieved via itsbinding surfaces.

It is therefore the object of the invention to further develop apressure-medium actuated friction disk clutch with the purpose ofimproving functional safety, of reducing cost of the used disk springsand of transmitting forces as high as possible with small spacerequirements, via the disk springs.

SUMMARY OF THE INVENTION

Now there has been developed a pressure-medium actuated friction diskclutch or brake comprising:

a cylinder;

a piston within the cylinder movable along an axis A;

a friction disk clutch adjacent the piston including a pressure plate;

a disk spring arranged between the piston and the pressure plate,respective binding surfaces being formed along faces of the piston andplate, the disk spring contacting the binding surfaces wherein adistance along a perpendicular to axis A between contact points on thebinding surfaces defines a lever arm, the binding surfaces beinggenerally perpendicular to axis A except that at least one of thebinding surfaces has a portion that deviates from perpendicularly bybeing contoured to form a successive pair of curves each defined by arespective first and second radius along a direction of axis A, andcontact between the disk spring and binding surface contour effecting acharacteristic force curve upon engagement of the disk clutch or brake.

While according to the state of the art such as in German Patents 25 40191 and 34 41 815 where specially produced disk springs are required,according to the present of the invention, standard springs can be usedand selected according to a characteristic curve of the spring. Thesestandard springs can be mass produced and therefore are inexpensive. Atthe same time these springs, are improved with respect to their servicelife. Since according to the invention, during the closing process ofthe friction disk clutch the effective lever arm is reduced between thebinding points of the disk spring, it is possible to use relatively thinsprings, which are particularly soft in the initial stage of the closingprocess and can thereby very well prevent impact effects, and asconsequence of the lever arm shortening during the closing stage becomesufficiently firm to transmit high forces, without completely losingtheir elasticity.

Starting with the pure characteristic curve of the spring, thecharacteristic force curve such a it is at the closing of the frictiondisk clutch, can be achieved only due to variable geometry at thebinding surfaces of the piston or also of the end plate. Both solutionscan be carried out simply and in a cost-effective manner. If differentradii are joined to form a curved binding surface, the effective leverarm is shortened between the binding surfaces of the disk spring becausethe contact point for instance rolls off on the radii. Therefore, thecharacteristic force line does not ascend linearly, but depends on theshortening of the lever arm. This way, the closing of the friction diskclutch starts out very gentle, while in the closed position of thefriction disk clutch high forces can be transmitted via the disk spring,whereby the disk springs can still afford a residual elasticity.

Of course the present invention is not intended to be limited to theexemplative specific features described. Those persons skilled in theart will from the invention description be directed to other embodimentsall of which are within the purview and scope of the invention.

BRIEF DESCRIPTION OF THE INVENTION

The above and other objects, advantages and features of the inventionwill become more readily apparent from the following description,reference being made to the accompanying highly diagrammatic drawing inwhich:

FIG. 1 is a friction disk clutch in half section,

FIG. 2 is a profile in expanded view of a binding surface of a diskspring against a piston surface,

FIG. 3 is further profile according to FIG. 2,

FIG. 4 is characteristic force line graph according to the profiledbinding surface from FIG. 2,

FIG. 5 is a force line graph according to the binding surface from FIG.3, and

FIG. 6 is a by-pass coupling in a torque converter.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates in half section a friction disk clutchconsisting of inner lamellae 6, outer lamellae 7, pressure plate 4, endplate 5, inner-lamellae carrier 8 and outer-lamellae carrier 9. Pressureplate 4 and end plate 5 are both non-rotationally supported in theouter-lamellae carrier 9. The friction disk clutch is actuated viapiston/cylinder actuation device 1, 2, whereby a pressure chamber 21 isclosed off by seals 12 located in piston 1. A disk spring 3 is providedbetween the piston 1 and the pressure plate 4.

Inner and outer lamellae 6, 7 and pressure plate 4 are supported axiallyslidably but non-rotatably in the inner-lamellae carrier 8 and theouter-lamellae carrier 9, while the end plate 5 is axially fastened atleast in one direction, by a grooved ring 91. A binding surface 11 ofthe piston 1 has a contour R1, R2 deviating from a right angle towardsan axis of rotation A, these contours being composed of certaingeometrical contours succeeding each other in radial direction tothereby create a binding surface curved in a radial direction.

FIG. 2 shows a first example of the binding surface 11 at the piston 1centeracting with disk spring 3, which inwardly adheres radially to thepiston 1 and outwardly adheres radially to an pressure plate 4. In thearea of the inner radial binding surface 11, disk spring 3 has anorientation deviating from a right angle relative to the axis directionAl and is defined by two radii R1, R2, succeeding each other in a radialdirection. This way, the contour of the binding surface 11 is composedof a small, radially internal radius R1, a of subsequently arrangedlarger radius R2 and of a straight line perpendicular to the axisdirection Al. The smaller radius leads over for instance, extends overan angle of 3° and the larger radius over an angle of 6°, so that thetangent Ta of the small radius R1 deviates by an angle of TA=9° from thestraight line of the binding surface 11. This angle has to be smallerthan the angle of attack TF, which results in the relaxed positionbetween the disk spring 3 and the straight line of the binding surface11 extending at a right angle to the axis direction A1.

FIG. 3 corresponds to FIG. 2, with the difference that the contour inthe area of the radial internal binding surface has in addition to thealready described radially internal small radius R1, also a very smallradius R4, e.g. of 0.5 mm, forming an offset 13. The common tangent Ta2of the radii R1 and R4 has thereby also to have an angle TaR4 to thevertical on the axis A.

FIG. 4 shows the characteristic force curve resulting from the contourof the binding surface 11 at the piston 1 according to FIG. 2. In andFIG. 5 is shown the characteristic force curve K2 which is representedaccording to the binding surface 11 in FIG. 3. The characteristic curvesof the disk springs are marked TK, and they establish themselves eachtime in accordance with the selected .dimensions of the used disksprings 3. Force P is repesented above the vertical and the pistontravel Kw along the horizontal axis. Kwl marks the point where thepiston 1, the disk spring 3, the pressure plate 4 and all inner- andouter lamellae 6 and 7 contact each other and to the end plate 5. Thecharacteristic force curve K1 in the path segment W1 results from theangle difference between the angle of the tangent Ta of the radius R1and the angle of attack TF of the disk spring 3 in the contact point 10.The continuation of this straight line is the characteristic line TK,which would be effective if the binding surface for instance on thepiston were to run at a right angle to the axis A of the friction diskclutch and not have any definitely shaped radially running contour, andthe contact point 10 were to remain in principle unchanged, at thispoint. The characteristic force curve K1 assigned to the path segment W2is created as a result of the change in the lever arm, which occurs whenthe disk spring 3 with its contact 10 rolls off small radius R1 of thecontour of the piston 1, while the piston continues to travel in theengagement direction. Due to the relatively small radius R1, the changein the lever arm and thereby the force increase is small, in arelatively long path. The steeper ascent of the characteristic forcecurve K1 in the path segment W3 results from the rolling-off of the diskspring 3 with the contact point 10 from the larger radius R2 of thecontour of the piston 1. The tangents of the radii R1 and R2 areidentical in the transition point of these two radii, so that betweenthe path segments W2 and W3 no offset occurs in the characteristic forcecurve. The large radius R2 causes a marked shortening of the lever armduring a small axial travel path of the piston 1, and thereby arelatively steeper force increase. At the point Kw2, the clutch is fullyclosed and transmits the full torque, whereby the disk spring is pressedtogether to approximately one quarter of its axial deflection. Through afree selection of a standard spring and through intentional selection ofthe configuration of at least one binding surface, e.g. the bindingsurface 11 of the piston 1, through an arrangement in succession ofdefined contours in radial direction it is possible to maintain anydesired characteristic force curve, e.g. K1, so that all intendedconditions are met when the clutch closes.

In the second embodiment example according to FIGS. 3 and 5, the courseof the first two marked path segments W1 and W2 is the same as alreadydescribed. However, the small radius R1 is selected larger i.e. R1according to FIGS. 2 and 4 is about 20 mm while R1 according to FIG. 3and 5 is about 36.5 mm. In this way, there is a steeper slope to thecharacteristic force curve K2 in the path segment W2 of FIG. 5. As shownin FIG. 3, an additional very small radius R4 is added so that thecontact point 10 in the closed position 100 does not roll off an furtherThus, the path segment 3 in FIG. 5 is a straight line which slopesrelatively steeply, whereby this slope is dependent on the effectivelever arm H1, which remains approximately constant for the rest of thepath. The pressure-medium actuated friction disk clutch, which of coursecan also be a friction disk brake, works as follows: Via thepressure-medium supply duct 22, a pressure medium is guided intopressure chamber 21 to actuate piston 1. Force is then applied by piston1 against disk spring 3 and pressure plate 4 which then brings togetherthe inner- and outer lamallae 7, 8 so that they rest against end plate5. Thereby the contact point Kwl according to FIGS. 4 and 5 is reached.Onward from point Kwl operation is dependent on the geometry resultingfrom the angle relationships, i.e. angle of attack TF of the disk spring3 and angle Ta, of the tangent Ta- from the binding surface 11 and thedisk spring 3. An increasing shortening of the lever arm results in anincreasing steepness of the characteristic curve of the spring and aprogressively increasing pressure P (moment) in the lamellar packet. Thecharacteristic force curve Kl, K2 of the path segment W1 correspondsapproximately to the characteristic spring curve TK of the selected diskspring 3. Depending on the contour of the binding surface , e.g. R1+R2according to FIGS. 2 and 4, or R1 +R4 according to FIGS. 3 and 5, thefrictional disk clutch is frictionally engaged for the transmission ofthe torque. Thereby, the clutch is in a simple manner adjustable to allload situation, only by selecting a simple disk spring--standardspring--and a suitable contour at the binding surface, e.g. 11. Byventing the pressure chamber 21, the friction disk clutch is opened,whereby in many application cases the generally known opening spring(not shown) is not required, because the disk spring 3 is arrangedbetween the piston 1 and the pressure plate 4. Particularly well suitedis the solution shown for the use as a by-pass coupling I in ahydrodynamic torque converter II, which is precedingly connected with atransmission III (FIG. 6).

The invention is not limited only to the features represented in theembodiment examples, but also includes variations thereof such as thebinding surface being arranged in the same sense on the pressure plate 4or having two binding surfaces, on the piston and on the pressure platewhich are shaped according to the invention. The embodiment of afriction disk brake according to the invention is not represented, sincein this case the same conditions result in connection with the bindingsurface at the piston, or pressure plate. As in the already describedfriction disk clutch, only the piston/cylinder- actuation device and theouter-lamellae carrier are mounted in or on stationary components, e.g.in or on a transmission housing.

We claim:
 1. A pressure-medium actuated friction disk clutch or-brakecomprising:a cylinder; a piston within said cylinder movable along anaxis a friction disk clutch adjacent the piston including a pressureplate; a disk spring arranged between said piston and said pressureplate, respective binding surfaces being formed along faces of saidpiston and said plate, said disk spring contacting said binding surfaceswherein a distance along a perpendicular to axis A between contactpoints on said binding surfaces defines a lever arm, said bindingsurfaces being generally perpendicular to axis A except that at leastone of said binding surfaces has a portion that deviates fromperpendicularity by being contoured to form a successive pair of curvesdefined by a respective first and second radius along a direction ofsaid axis, and contact between said disk spring and binding surfacecontour between said disk spring and binding surface contour effecting acharacteristic force curve upon engagement of the disk clutch or-brake;said characteristic force curve for a travel path of said piston betweenan initial contact point and a final contact point indicating a closedclutch position being defined by:an angular difference between a tangentof said first radius at said initial contact point and an angle ofattack, said angle of attack being formed between a major outer surfaceof said spring disk and said perpendicular binding surface of saidpiston; a change in said lever arm distance measured from said firstradius which is the smaller of said two radii; and a change in saidlever arm distance measured from said second radius which is the largerof said two radii.
 2. A pressure-medium actuated friction disk clutchor-brake comprising:a cylinder; a piston within said cylinder movablealong an axis A; a friction disk clutch adjacent the piston including apressure plate; a disk spring arranged between said piston and saidpressure plate, respective binding surfaces being formed along faces ofsaid piston and said plate, said disk spring contacting said bindingsurfaces wherein a distance along a perpendicular to axis A betweencontact points on said binding surfaces defines a lever arm, saidbinding surfaces being generally perpendicular to axis A except that atleast one of said binding surfaces has a portion that deviates fromperpendicularity by being contoured to form a successive pair of curvesdefined by a respective first and second radius along a direction ofsaid axis, and contact between said disk spring and binding surfacecontour effecting a characteristic force curve upon engagement of thedisk clutch or-brake; said binding surface of said piston having anoffset segment fashioned as a radially oriented curved recesstherewithin; said characteristic force curve for a travel path of saidpiston between in initial contact point and a final contact pointindicating a closed clutch position being defined by:an angulardifference between a tangent of said first radius at said initialcontact point and an angle of attack, said angle of attack being formedbetween a major outer surface of said spring disk and said perpendicularbinding surface of said piston; a change in said lever arm distancemeasured from said first radius which is the smaller of said two radii;and an almost constant, relatively small lever arm whose distance ismeasured starting from a second contact point, said second contact pointbeing at a transition point of curvature demarking a border of saidcurved recess.